Fabrication method for spin valve sensor with insulating and conducting seed layers

ABSTRACT

A method is described comprising forming an insulating polycrystalline seed layer in a first chamber by reactively pulsed DC magnetron sputtering, then forming an insulating amorphous-like seed layer in a second chamber by reactively pulsed DC magnetron sputtering, then forming a conducting seed layer and a ferromagnetic free layer in a third chamber by ion beam sputtering, and then forming the remainder of a spin valve sensor through the antiferromagnetic layer in a fourth chamber by DC magnetron sputtering.

[0001] The present application is a Divisional of a NonprovisionalApplication filed on Dec. 8, 2000, and assigned application Ser. No.09/733,876, which is a Continuation-In-Part of a NonprovisionalApplication filed on Aug. 31, 2000, and assigned application Ser. No.09/652,767.

FIELD OF THE INVENTION

[0002] The field of invention relates to giant magnetoresistance (GMR)head technology generally; and more specifically, to techniques that maybe used to forming high read sensitivity heads via seed layerprocessing.

BACKGROUND

[0003] Hardware systems often include memory storage devices havingmedia on which data can be written to and read from. A direct accessstorage device (DASD or disk drive) incorporating rotating magneticdisks are commonly used for storing data in a magnetic form. Magneticheads, when writing data, record concentric, radially spaced informationtracks on the rotating disks.

[0004] Magnetic heads also typically include read sensors that read datafrom the tracks on the disk surfaces. In high capacity disk drives,magnetoresistive (MR) read sensors, the defining structure of MR heads,can read stored data at higher linear densities than thin film heads. AnMR head detects the magnetic field(s) through the change in resistanceof its MR sensor. The resistance of the MR sensor changes as a functionof the strength of magnetic fields that emanates from the rotating disk.

[0005] One type of MR sensor, referred to as a giant magnetoresistance(GMR) sensor, takes advantage of the GMR effect. In the GMR sensor, theresistance of the GMR sensor varies with the strength of magnetic fieldsfrom the rotating disk and as a function of the spin dependenttransmission of conducting electrons between ferromagnetic layersseparated by a nonmagnetic layer (commonly referred to as a spacerlayer) and the accompanying spin dependent scattering within theferromagnetic layers that takes place at the interface of the magneticand nonmagnetic layers.

[0006] GMR sensors using two layers of ferromagnetic material separatedby a layer of GMR promoting nonmagnetic material (the spacer layer) aregenerally referred to as spin valve (SV) sensors. In an SV sensor, oneof the ferromagnetic layers, referred to as the pinned layer, has itsmagnetization “pinned” via the influence of exchange coupling to anantiferromagnetic layer. Due to the relatively high unidirectionalanisotropy field (H_(UA)) associated with the pinned layer, themagnetization of the pinned layer typically does not rotate with respectto the magnetic flux lines that emanate/terminate from/to the rotatingdisk. The magnetization of the other ferromagnetic layer (commonlyreferred to as a ferromagnetic free layer), however, is free to rotatewith respect to the magnetic flux lines that emanate/terminate from/tothe rotating disk.

[0007]FIG. 1 shows a prior art SV sensor 100 comprising a seed layer 102formed upon a gap layer 101. The seed layer 102 helps form properlymicrostructures of the layers formed thereon. Over seed layer 102 is aferromagnetic free layer 103. An antiferromagnetic (AFM) layer 105 isused to pin the magnetization of the pinned layer 104. Pinned layer 104is separated from ferromagnetic free layer 103 by the nonmagnetic, GMRpromoting, spacer layer 119. Note that the ferromagnetic free layer 103may have a multilayered structure with two or more ferromagnetic layers.

[0008]FIG. 2 shows another prior art SV sensor 200 where the pinnedlayer is implemented as a structure 220 having two ferromagnetic films221, 222 (also referred to as AP2 and AP1 layers, respectively)separated by a nonmagnetic film 223 (such as ruthenium Ru) that providesantiparallel (AP) exchange coupling of the two ferromagnetic films 221,222. The spin valve sensor such as that 200 shown in FIG. 2 is referredto as a synthetic spin valve sensor in light of its synthetic structurebased on the antiparallel exchange-coupling relationship between films221, 222.

[0009]FIG. 2 shows a synthetic spin valve sensor 200 comprising a seedlayer 202 formed upon a gap layer 201. The seed layer 202 helps formproperly microstructures of the layers formed thereon. Over the seedlayer 202 is a ferromagnetic free layer 203. An antiferromagnetic (AFM)layer 205 are used to pin the magnetization of the AP2 layer 221. An AP1layer 222 is separated from the ferromagnetic free layer 203 by a spacerlayer 204. Note that ferromagnetic free layer 203 may have amultilayered structure with two or more ferromagnetic layers.

[0010] Problems with forming the sensors 100, 200 shown in FIGS. 1 and 2include forming the seed layer 102, 202 with a microstructure thatsuitably influences the microstructure of the AFM layer 105, 205 as wellas the other layers. Since the microstructure of the AFM layer 105, 205(in light of its material composition) as well as the microstructure ofthe other layers affect the GMR properties of the spin valve sensor, thequality of the read sensitivity of the spin valve sensor 100, 200depends upon the techniques used to form the seed layer 102, 202.

SUMMARY OF INVENTION

[0011] A method is described comprising forming an insulatingpolycrystalline seed layer in a first chamber by reactively pulsed DCmagnetron sputtering, then forming an insulating amorphous-like seedlayer in a second chamber by reactively pulsed DC magnetron sputtering,then forming a conducting seed layer and a ferromagnetic free layer in athird chamber by ion beam sputtering, and then forming the remainder ofa spin valve sensor through the antiferromagnetic layer in a fourthchamber by DC magnetron sputtering.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] The present invention is illustrated by way of example, and notlimitation, in the Figures of the accompanying drawings in which:

[0013]FIG. 1 shows a simple spin valve sensor (prior art).

[0014]FIG. 2 shows a synthetic spin valve sensor (prior art).

[0015]FIG. 3a shows a multilayered seed structure.

[0016]FIG. 3b shows a diagram of a manufacturing tool 300 that may beused to form a multilayered seed structure.

[0017]FIG. 4 shows a method 400 that may be used to form spin valvesensors with a multilayered seed structure.

[0018]FIG. 5 shows MR responses of simple Ni—Mn spin valve sensors withvarious seed layers.

[0019]FIG. 6 shows MR responses of synthetic Ni—Mn spin valve sensorswith various seed layers.

[0020]FIG. 7 shows H_(F) vs. Cu spacer layer thickness for simple Ni—Mnspin valve sensors comprising seedlayers/Ni—Fe(4.5)/Co—Fe(0.6)/Cu(2.4)/Co(3.2)/Ni—Mn(25)/Ta(6) films. Theseed layers are Ta(3), NiMnO_(x)(3), NiO(33)/Cu(1.4) andNiO(33)/NiMnO_(x)(3)/Cu(1.4) films.

[0021]FIG. 8 shows ΔR_(G)/R_(//) vs Cu spacer layer thickness for simpleNi—Mn spin valve sensors comprising seedlayers/Ni—Fe(4.5)/Co—Fe(0.6)/Cu(2.4)/Co(3.2)/Ni—Mn(25)/Ta(6) films. Theseed layers are Ta(3), NiMnO_(x)(3), NiO(33)/Cu(1.4) orNiO(33)/NiMnO_(x)(3)/Cu(1.4) films.

[0022]FIG. 9 shows in plane x-ray diffraction patterns of simple Ni—Mnspin valve sensors with Ta layers before and after anneal for 2 h at280° C.

[0023]FIG. 10 shows in plane x-ray diffraction patterns of simple Ni—Mnspin valve sensors with NiO/NiMnO_(x)/Cu seed layers before and afteranneal for 2 h at 280° C.

[0024]FIG. 11 shows a method 1000 that may be alternatively used to formspin valve sensors with a multilayered seed structure.

[0025]FIG. 12 shows MR responses of simple Pt—Mn spin valve sensors withvarious seed layers.

[0026]FIG. 13 shows MR responses of synthetic Pt—Mn spin valve sensorswith various seed layers.

[0027]FIG. 14 shows H_(F) vs Cu spacer layer thickness for syntheticPt—Mn spin valve sensors comprising seedlayers/Ni—Fe(3)/Co—Fe(0.9)/Cu/Co—Fe(2.8)/Ru(0.8)/Co—Fe(2.4)/Pt—Mn(22.5)/Ta(6)films. The seed layers are Ta(3), Ni—Cr—Fe(3), NiO(3)/Ni—Cr—Fe(3) orAl₂O₃(3)/Ni—Fe—Cr(3) films.

[0028]FIG. 15 shows ΔR_(G)/R_(//) vs Cu spacer layer thickness forsynthetic Pt—Mn spin valve sensors comprising seedlayers/Ni—Fe(3)/Co—Fe(0.9)/Cu/Co—Fe(2.8)/Ru(0.8)/Co—Fe(2.4)/Pt—Mn(22.5)/Ta(6)films. The seed layers are Ta(3), Ni—Cr—Fe(3), NiO(3)/Ni—Cr—Fe(3) orAl₂O₃(3)/Ni—Fe—Cr(3) films.

[0029]FIG. 16 shows in plane x-ray diffraction patterns of the syntheticPt—Mn spin valve sensor with the Ta seed layer before and after annealfor 4 h at 260° C.

DETAILED DESCRIPTION

[0030] A method is described comprising forming an insulatingpolycrystalline seed layer in a first chamber by reactively pulsed DCmagnetron sputtering, then forming an insulating amorphous-like seedlayer in a second chamber by reactively pulsed DC magnetron sputtering,then forming a conducting seed layer and a ferromagnetic free layer in athird chamber by ion beam sputtering, and then forming the remainder ofa spin valve sensor through the antiferromagnetic layer in a fourthchamber by DC magnetron sputtering.

[0031] These and other embodiments of the present invention may berealized in accordance with the following teachings and it should beevident that various modifications and changes may be made in thefollowing teachings without departing from the broader spirit and scopeof the invention. The specification and drawings are, accordingly, to beregarded in an illustrative rather than restrictive sense and theinvention measured only in terms of the claims.

[0032] Sensors 100, 200 are impacted as disk storage systems continue toincrease the density at which they store bits of information. As disksare configured to store increasing amounts of information, the strengthof magnetic fields that emanate/terminate from/to the disk surfacebecome weaker and weaker. In order to detect these weaker fields,sensors 100, 200 should be designed with enhanced read sensitivity atsmaller dimensions.

[0033] Enhanced read sensitivity at a smaller dimension may be achievedby: 1) keeping the ferromagnetic exchange-coupling field H_(F) betweenthe ferromagnetic free layer 103, 203 and the pinned layers 104, 220small (e.g., below 10 Oersteads (Oe)) so that the magnetization of theferromagnetic free layer 103, 203 lies along the z axis as seen in FIGS.1 and 2; 2) keeping the unidirectional anisotropy field (H_(UA)) betweenthe pinned layer 102, 220 and the AFM layer 105, 205 high (e.g., above600 Oe) so that the magnetization of the pinned layer 102, 220 liesalong the y axis as seen in FIGS. 1 and 2; and 3) forming a spin valvesensor with a large giant magnetoresistive coefficient.

[0034] If the ferromagnetic exchange-coupling field H_(F), between theferromagnetic free layer 103, 203 and the pinned layers 102, 220 is toolarge, the magnetization of the ferromagnetic free layer will beadversely biased in a direction (e.g., having a + or − y directioncomponent) that reduces the output signal swing of the spin valve sensor100, 200. Similarly, if the unidirectional anisotropy field (H_(UA))between the pinned layer 102, 220 and the AFM layer 105, 205 is toosmall, the magnetization of the pinned layer 102, 220 may also have anadverse bias in a direction (e.g., having a + or − z directioncomponent) that also reduces sensor output signal swing. Reduced outputsignal swing from the spin valve sensor 100, 200 corresponds to reducedread sensitivity and is therefore undesirable for highly sensitivesensors.

[0035] Achieving a sufficiently small coupling field H_(F), may be atleast partially accomplished by controlling the microstructure of thefree, spacer and pinned layers. Specifically, H_(F) is reduced as thesurface roughness of these layers decrease and the densities of theselayers increase. Referring to FIGS. 1 and 2, the multilayered sensorstructure 100, 200 is formed, layer by layer, in the +x direction. Thus,layer thickness and roughness are measured along the x axis. The densityof a layer is measured by how tightly packed the grains of the layerare. Producing adequately smooth and adequately dense free, spacer andpinned layers allows H_(F) to be tightly controlled and minimized.

[0036] A sufficiently large unidirectional anisotropy field (H_(UA)) isproduced by forming the AFM layer with a face-centered-tetragonal (fct)phase. Materials used for the AFM layer 105, 205, such as Ni—Mn andPt—Mn, are nonmagnetic if formed in a face-centered-cubic (fcc) phase.Since AFM layers 105, 205 are typically formed initially in anonmagnetic fcc phase, the sensor is subsequently annealed to transformthe phase of the AFM layer from a nonferromagnetic fcc phase to anantiferromagnetic fct phase.

[0037] It has been found, however, that the initial fcc orientation ofthe AFM layer 105, 205 affects the extent to which the AFM layer 105,205 is able to transform to an fct phase. Specifically, {220} texturedfcc Ni—Mn films are not easily annealed into an fct phase. An initialfcc texture of {200}, however, allows the Ni—Mn film 105, 205 to moreeasily transform into an fct phase.

[0038] The seed layer 102, 202 may be used to: 1) reduce the surfaceroughness of the sensor layers (to reduce H_(F)); and 2) induce a {200}fcc crystalline texture in the AFM layer 105, 205 so that the fcc phasemay be more easily transformed into an fct phase during anneal. Thecrystalline structure of a layer formed upon another layer is influencedby the lower crystalline structure. Specifically, the upper layer tendsto form with the crystalline structure of the lower layer. If the seedlayer 102, 202 is formed with a {200} crystalline texture, the remaininglayers atop the seed layer 102, 202, (including the AFM layer 105, 205)will tend to be formed in a {200} crystalline texture. Thus, the AFMlayer 105, 205 may be initially formed with a {200} crystalline textureif the seed layer 102, 202 is formed with a {200} crystalline texture.

[0039] Thus an approach to forming a highly sensitive sensor is to formsmooth seed layers having a {200} crystalline texture. Additionalconsiderations for a seed layer include spin filtering and thermalstability. Thermal stability relates to the ability of a sensor tomaintain adequate sensitivity after one or more anneal steps duringmanufacturing. Because of the various concerns involved (smoothness,{200} crystalline texture, spin filtering, thermal stability, etc.) amultilayered seed structure may be used. In a multilayered seedstructure approach, individual layers may be used to address at leastone of the designer's concerns. In one approach, shown in FIG. 3a, amultilayer seed structure 310 having a first insulating layer 311, asecond insulating layer 312, and a third conducting layer 313, isformed. A fourth conducting layer 314 may be added as well. The firstand second insulating layers 311, 312 are used to provide a {200}crystalline texture and adequate smoothness

[0040] In one embodiment, the first insulating layer 311 ispolycrystalline and the second insulating layer 312 is amorphous-like.For example, a polycrystalline oxide layer (e.g., NiO) may correspond tothe first insulating layer 311 and an amorphous-like oxide layer (e.g.,NiMnO_(x)) may correspond to the second insulating layer 312.

[0041] The third conducting layer 313 may be formed with a materialhaving low electrical resistivity (e.g., Cu) to provide spin filtering.The fourth conducing layer 314, may be used to promote epitaxial growthof the ferromagnetic free layer 315 and should have the same or similarlattice spacing(s) or structure as the ferromagnetic free layer 315 toprovide good lattice matching with the ferromagnetic free layer 315.

[0042] Note that the third and fourth conducting layers 313, 314 isolatethe insulating layers 311, 312 from the ferromagnetic free layer 315. Ithas been observed that the insulating layers 311, 312 adversely affectthe thermal stability of the sensor if allowed to come in contact withthe ferromagnetic free layer 315. Thus having one or more conductinglayers between the ferromagnetic free layer and insulating layerpromotes the thermal stability of the sensor.

[0043]FIG. 3b shows a diagram of a manufacturing tool 300 that may beused to form the multilayered seed structure 102, 202 as well as therest of the sensor 100, 200 as shown in FIGS. 1 and 2. The tool 300 hasat least four chambers used for forming various layers associated withthe sensors 100, 200 shown in FIGS. 1 and 2 and the seed layer 310 shownin FIG. 3a. Both the first and second chambers 301, 302 are DC magnetronsputtering chambers. The third chamber 303 is an ion beam sputteringchamber. The fourth chamber 304 is a third DC magnetron sputteringchamber. All four chambers 301 through 304 are coupled together by atransport module 305. Transport module 305 is used to transport a waferhaving a plurality of sensors, during manufacturing, from chamber tochamber.

[0044] In an embodiment, the first two DC magentron sputtering chambers301, 302 are single target sputtering chambers while the ion beam andthird DC magnetron sputtering chambers 303, 304 are multitargetsputtering chambers. The discussion below refers to such a tool 300embodiment, however, note that multitarget chambers may be used forchambers 301, 302 to implement the method 400 shown in FIG. 4. Also, asan alternative embodiment (not shown in any Figure), different layers ofa multilayered seed structure formed with reactively pulsed DC magnetronsputtering (e.g., NiO and NiMnO_(x)) may be formed in a single,multitarget DC magnetron sputtering chamber.

[0045]FIG. 4 shows a method 400 that may be used to form sensors with amultilayered seed structure 310 such as NiO/NiMnO_(x)/Cu seed layerscorresponding to layers 311/312/313 of FIG. 3a. Referring to FIGS. 3a, band 4, the first layer 311 of the seed layer structure 310 (e.g., NiO)is formed 401 in one of the single target DC magnetron sputteringchambers (e.g., chamber 301). After forming the insulatingpolycrystalline seed layer in a single target DC magnetron sputteringchamber 301, the insulating amorphous-like seed layer 312 (e.g.,NiMnO_(x)) is formed 402 in the other single target DC magnetronsputtering chamber (e.g., chamber 302). Note this requires the wafer tomove through the transport module 305 as the insulating polycrystallineseed layer is passed from the first chamber 301 to the second chamber302.

[0046] After the insulating amorphous-like seed layer 312 is formed inthe second chamber 302, the sensor structure is formed 403 up to thecompletion of the ferromagnetic free layer 315 within the multitargetion beam sputtering chamber 303. For sensors having four seed layers,the third 313 and fourth 314 seed layers and the ferromagnetic freelayer 315 are both formed 403 in the multitarget ion beam sputteringchamber 303. Since the ferromagnetic free layer 103, 203 is formed withferromagnetic material(s) (such as Ni—Fe and/or Co—Fe) and the third 313and fourth 314 seed layers are typically formed with metallic materials,different targets comprising the different employed materials should beused. Note that a multilayered ferromagnetic free layer structure 103,203 is possible. An example includes an embodiment where the firstferromagnetic free layer material (that is formed upon the seed layer)is Ni—Fe and a second ferromagnetic free layer material (formed upon theNi—Fe layer) is Co—Fe.

[0047] The combination of targets used to form the layers deposited inthe ion beam sputtering chamber 303 (e.g., a Cu target, a Ni—Fe targetand a Co—Fe target) should be fixed on a rotatable drum in the chamber303 in such a manner that a particular target used for a particularlayer may be effectively moved by rotating the drum towards the openingof a shutter in the chamber 303 for the deposition of its correspondinglayer.

[0048] For a simple spin valve sensor such as sensor 100 of FIG. 1,after the ferromagnetic free layer 103 is formed 403 in the ion beamsputtering chamber 303, the spacer layer 119 is formed in themultitarget DC magnetron sputtering chamber 304. In a furtherembodiment, the remainder of the spin valve sensor including the pinnedlayer 104 and AFM layer 105 are formed 404 in the multitarget DCmagnetron sputtering chamber 304. In one such further embodiment, thespacer layer 119 is Cu, the pinned layer 104 is Co and the AFM layer 105is Ni—Mn. A cap material such as Ta may be formed over the AFM layer 105in chamber 304 as well.

[0049] For a synthetic spin valve sensor such as sensor 200 of FIG. 2,after the ferromagnetic free layer 203 is formed 403 in the ion beamsputtering chamber 303, in another further embodiment; the spacer layer204, AP1 layer 222, nonmagnetic layer 223, AP2 layer 221 and AFM layer205 are all formed 404 in the multitarget DC magnetron sputteringchamber 304. In an embodiment; the spacer layer 204 is Cu, the AP1 layer222 is Co, the nonmagnetic layer 223 is Ru, the AP2 layer 221 is Co andthe AFM layer 105 is Ni—Mn. Again, a cap material such as Ta may beformed over the AFM layer 105 in chamber 304 as well.

[0050] Reviewing FIG. 4 to summarize then: 1) an insulatingpolycrystalline seed layer 311 is formed 401 in a first DC magnetronsputtering chamber 301; 2) an insulating amorphous-like seed layer 312is formed 402 in a second DC magnetron sputtering chamber 302; 3) aconducting seed layer 313 and ferromagnetic free layer 315 are formed403 in an ion beam sputtering chamber 303 (a fourth seed layer 314 mayalso be formed in the ion beam sputtering chamber 303); and 4) thespacer layer is then formed 404 in another DC magetron sputteringchamber 304 (the remaining sensor structure up through theantiferromagnetic layer or cap layer may also be formed 404 in the otherDC magnetron sputtering chamber 404). The following discussion providesmore details concerning embodiments of the method 400 of FIG. 4.

[0051] In an embodiment, the first 311 and second 312 seed layers areinsulating. The insulating seed layer 311 may also be polycrystallineand the insulating seed layer 312 may also be amorphous-like. The seedlayer 313 may also be conductive and the fourth seed layer 314 may havea structure or lattice spacing similar to the ferromagnetic free layer315 to promote epitaxial growth of the ferromagnetic free layer 315.

[0052] With respect to the deposition 401 of the first film, in anembodiment a NiO polycrystalline film is deposited within a first singletarget DC sputtering chamber 301 on an Al₂O₃ coated wafer with reactivepulsed-DC magnetron sputtering from a metallic Ni target in 1 mTorr ofmixed argon and oxygen gases. An asymmetric bipolar pulsed DC powersupply is used to provide alternating target voltages of oppositepolarities such as alternating voltages of −200 and +50 V.

[0053] When a first voltage of a first negative polarity (e.g., −200 V)is applied to the Ni target, argon ions are accelerated into the Nitarget with a sufficient kinetic energy to knock Ni atoms from the Nitarget. The freed Ni atoms subsequently collide with oxygen whentraveling in the plasma, forming a NiO film on the Al₂O₃ coated wafer.Note that a NiO film may also be deposited onto the Ni target, forming acapacitor between the Ni target and the plasma. If the first negativepolarity voltage (e.g., −200 V) continues to be applied to the Nitarget, current will eventually cease flowing through the NiO capacitorwhich will cease the sputtering activity. At this point, the target is“poisoned”.

[0054] Sputtering may be continued if the polarity of the target voltageis reversed to a second voltage of positive polarity (e.g., from −200 to+50 V). When the second voltage of positive polarity is applied to thetarget, the NiO capacitor is charged to a positive polarity (e.g., +50V) on the surface exposed to the plasma. When the voltage returns to thefirst polarity (e.g., −200 V), the voltage on the plasma side of the NiOcapacitor remains at the first polarity (e.g., −250 V). With this extraenergy, the NiO film is sputtered off from the Ni target, allowing forthe sputtering to continue.

[0055] A reactively DC-pulsed sputtered NiO film as the initial seedlayer provides a smooth interface on which the sensor grows. Asdiscussed, sensor layers formed with reduced surface roughness (and highdensity) keep the ferromagnetic exchange-coupling field H_(F) betweenthe ferromagnetic free layer 103, 203 and the pinned layer 104, 220small.

[0056]FIG. 5 and Table 1 show easy axis MR responses and GMR propertiesof simple spin valve sensors comprising seedlayers/Ni—Fe(4.5)/Co—Fe(0.6)/Cu(2.4)/Co(3.2)/Ni—Mn(25)/Ta(6) films afteranneal for 2 at 280° C. with a field of 800 Oe in a high vacuum oven,where the seed layers are Ta(3), NiMnO_(x)(3), NiO(33)/Cu(1.4) orNiO(33)/NiMnO_(x)(3)/Cu(1.4) films. TABLE 1 Magnetic and GMR propertiesof simple Ni—Mn spin valve sensors with various seed layers.NiO/NiMnO_(x)/ Properties Ta NiMnO_(x) NiO/Cu Cu H_(F) (Oe) 7.4 11.225.6 2.7 H_(UA) (Oe) 76 412 468 590 R_(//) (Ω/Y) 19.8 18.2 17.0 16.9ΔR_(G)/R_(//)(%) 5.8 6.8 8.5 9.4

[0057]FIG. 6 and Table 2 show easy-axis MR responses and GMR propertiesof synthetic spin valve sensors comprising seedlayers/Ni—Fe(4.5)/Co—Fe(0.6)/Cu(2.4)/Co(3.2)/Ru(0.8)/Co(3.2)/Ni—Mn(25)/Ta(6)films after anneal for 10 h at 260° C. with a field of 10 kOe in a highvacuum oven, where the seed layers are Ta(3), NiMnO_(x)(3),NiO(33)/Cu(1.4) or NiO(33)/NiMn_(x)(3)/Cu(1.4) films. Both the simpleand synthetic Ni—Mn spin valve sensors with the NiO/NiMnO_(x)/Cu seedlayers exhibits magnetic and GMR properties far better than those ofNi—Mn spin valve sensors with other seed layers. TABLE 2 Magnetic andGMR properties of synthetic Ni—Mn spin valve sensors with various seedlayers. NiO/NiMnO_(x)/ Properties Ta NiMnO_(x) NiO/Cu Cu H_(F) (Oe) 3.25.5 20.6 5.6 H_(UA) (Oe) 1735 1903 2206 2098 R_(//) (Ω/Y) 18.7 16.2 15.215.3 GMR (%) 4.3 6.6 7.7 8.1

[0058]FIGS. 7 and 8 show H_(F) and ΔR_(G)/R_(//), respectively, vs Cuspacer layer thickness for simple spin valve sensors comprising seedlayers/Ni—Fe(4.5)/Co—Fe(0.6)/Cu/Co(3.2)/Ni—Mn(25)/Ta(6) films afteranneal with a field of 800 Oe for 2 at 280° C., where the seed layersare Ta(3), NiMnO_(x)(3), NiO(33)/Cu(1.4) or NiO(33)/NiMnO_(x)(3)/Cu(1.4)films. The use of the NiO/NiMnO_(x)/Cu seed layers causes a substantialH_(F) oscillation with the Cu spacer layer thickness, thereby leading toan H_(F) of as low as 2.7 Oe when the Cu spacer layer is as thin as 2.4nm. In addition, the simple Ni—Mn spin valve with the NiO/NiMnO_(x)/Cuseed layers exhibits a ΔR_(G)/R_(//) much higher than those with otherseed layers.

[0059]FIG. 9 shows in-plane x-ray diffraction patterns of the simpleNi—Mn spin valve sensor with the Ta(3) seed layer before and afteranneal. Before and after anneal, the Ni—Fe films exhibit a {220}_(fcc)crystalline texture. Due to epitaxial growth, the Co—Fe, Cu, Co andNi—Mn films deposited thereon also exhibit a {220}_(fcc) crystallinetexture. In addition, the Ni—Mn film also exhibits a weak {111}_(fcc)crystalline texture. No phase transformation can be identified fromthese x-ray diffraction patterns.

[0060]FIG. 10 shows in-plane x-ray diffraction patterns of the simpleNi—Mn spin valve sensor with the NiO(33)/NiMnO_(x)(3)/Cu(1.4) seedlayers before and after anneal, where the NiO film is deposited withreactive DC magnetron sputtering. Before anneal, the NiO film exhibits astrong {200}_(fcc) crystalline texture, a weak {200}_(fcc) crystallinetextures, and an even weaker {111}_(fcc) crystalline texture. Due toepitaxial growth, the Ni—Fe, Co—Fe, Cu, Co and Ni—Mn films depositedthereon also exhibit {200}_(fcc), {220}_(fcc) and {111}_(fcc)crystalline textures. It should be noted that these films exhibit veryweak {111}_(fcc) crystalline textures. The strong peak shown at 42.8° infact mainly comes from the NiO {002}_(fcc) crystalline texture. Thisidentification is confirmed from other x-ray diffraction patterns ofsimilar spin valve sensors but with various NiO and Ni—Mn filmthicknesses. After anneal, the Ni—Mn {200}_(fcc) peak is split into(200)_(fct), (020)_(fct) and (002)_(fct) peaks, while the Ni—Mn{220}_(fcc) peak is also split into (220)_(fct), (202)_(fct) and(022)_(fct) peaks. These findings indicate that the transformation froman fcc phase (a=0.3685 nm) to an fct phase (a=0.3727 nm and c=0.3581 nm)has occurred in the Ni—Mn film. This peak splitting indicates that asmall amount of the fct phase nuclei may exist before anneal and itstarts to grow from its original matrix during anneal. The existence ofthe fct phase before anneal is supported by the fact that the Co andNi—Mn films have already exchange-coupled (H_(UA)≈10 Oe) before anneal.

[0061] It should be noted that if the NiO film is deposited with RFmagnetron sputtering from a ceramic NiO target in an argon gas, insteadof with reactive pulsed-DC magnetron sputtering, the NiO film onlyexhibits a strong {111})_(fcc) crystalline texture.

[0062] Previously described experimental results indicate that thefabrication method of the simple and synthetic Ni—Mn spin valve sensorswith the NiO/NiMnO_(x)/Cu seed layers leads to a low H_(F), a highH_(UA), a high GMR coefficient, and good soft magnetic properties of theferromagnetic free layer.

[0063] The use of reactive DC-pulsed magnetron sputtering for thedeposition of the NiO film causes the NiO film to exhibit a strong{002}_(fcc) crystalline texture. Due to epitaxial growth, the Ni—Mnfilms also exhibit a {002}_(fcc) crystalline textures. This Ni—Mn{002}_(fcc) crystalline texture appears to play a crucial role inaccelerating the phase transformation from the fcc phase to the fctphase and thus in attaining a high H_(UA). In addition, as the NiO filmthickness increases, the (200)_(fct), (020)_(fct), and (002)_(fct) peakintensities of the Ni—Mn film have been found to increase, while H_(UA)and ΔR_(G)/R_(//) has also been found to increase.

[0064] In contrast, if the NiO film is deposited with RF magnetronsputtering from a ceramic NiO target in an argon gas, it only exhibits astrong {111}_(fcc) crystalline textures. The lack in the {200}_(fcc)crystalline texture may cause difficulties in carrying out the phasetransformation, thus leading to a low H_(UA) and a low ΔR_(G)/R_(//).

[0065] The use of reactive DC-pulsed magnetron sputtering for thedeposition of the NiMnO_(x) film leads the NiMnO_(x) film to provide anin-situ smooth surface. Due to this in-situ smooth surface, H_(F)oscillates with the Cu spacer layer thickness, and an H_(F) of as low as2.7 Oe and a GMR coefficient of as high as 9.4% can be attained when theCu spacer layer is as thin as 2.4 nm.

[0066] In contrast, if the NiMnO_(x) film is exposed to air and the spinvalve sensor films are deposited later, the resultant ex-situ surfacedoes not lead to such good GMR properties.

[0067] The use of ion beam sputtering for the deposition of the Cu seedlayer causes the Cu seed layer to provide in-situ protection for theferromagnetic free layer from the deterioration of soft magneticproperties and thermal stability (resulting from to the direct contactbetween the insulating seed layer and the ferromagnetic free layer). Forexample. the use of the Cu seed layer substantially causes a reductionin a uniaxial anisotropy field (H_(K)) from 16 Oe to 7 Oe. Thisreduction will lead to an improvement in the permeability of theferromagnetic free layer. In fact, DC magnetron sputtering can also beused for the deposition of the Cu seed layer for the same purposes.However, since the electrical resistivity of the ion beam sputtered Cufilm (3.5 μΩ-cm) is higher than that of DC magnetron sputtered Cu film(2.8 μΩ-cm), ion beam sputtering is preferred to attain a high sensorresistance. More importantly, cycle time for the manufacture can besubstantially reduced since there is no need in transporting the waferfrom the ion beam chamber to the DC magnetron chamber, and then to theion beam chamber.

[0068] The use of ion beam sputtering for the deposition of Ni—Fe andCo—Fe films causes the spin valve sensor to exhibit a low H_(F). Forexample, the simple Ni—Mn spin valve sensor with ion beam sputteredNi—Fe/Co—Fe films exhibits an H_(F) of 2.7 Oe, while that with DCmagnetron sputtered Ni—Fe/Co—Fe films exhibits an H_(F) of beyond 10 Oe.The H_(F) can even reach zero or slightly negative (indicatingantiparallel ferromagnetic exchange-coupling across the Cu spacer layer)as the thickness of the ion beam sputtered Ni—Fe/Co—Fe films increasesto 6 nm. Such a low H_(F) is attained mainly due to the in-situ smoothsurface and partially due to that ion beam sputtering provides a denserfilm with less pinholes than DC magnetron sputtering.

[0069] The use of DC magnetron sputtering for the deposition of the Cuspacer layer causes the Cu spacer layer to exhibit an electricalresistivity lower than the use of ion beam sputtering. This lowelectrical resistivity leads to a high GMR coefficient. For example, theNi—Mn spin valve sensor with DC magnetron sputtered Cu spacer layerexhibit a ΔR_(G)/R_(//) of 9.4%, while Ni—Mn spin valve sensor with ionbeam sputtered Cu spacer layer exhibits a ΔR_(G)/R_(//) of 8.2%.

[0070] The use of DC magnetron sputtering for the deposition of Co andNi—Mn films causes the annealed Co/Ni—Mn films to exhibit an H_(UA) ofas high as 590 Oe. If the DC magnetron sputtered Co/Ni—Mn films arereplaced by ion beam sputtered Co/Ni—Mn films, H_(UA) is only around 450Oe. This difference in H_(UA) results from the fact that the DCmagnetron sputtered Ni—Mn film has a Mn content less by ˜1 at % than theNi—Mn target, while the ion beam sputtered Ni—Mn film has a Mn contentless by around ˜3 at % than the Ni—Mn target.

[0071] The use of DC magnetron sputtering for the deposition of Co, Ruand Co films causes the Co/Ru/Co films to exhibit a high spin-flopsaturation field (H_(S)) of ˜6 kOe. If the DC magnetron sputteredCo/Ru/Co films are replaced by ion beam sputtered Co/Ru/Co films, H_(S)is only around ˜2 kOe.

[0072] Referring back to FIG. 4, note that the method 400 of FIG. 4 maybe simplified to the method 1000 of FIG. 11 if two seed layers need notbe formed by reactively pulsed DC magnetron in separate chambers. In themethod 1000 of FIG. 11 a seed layer is formed 1001 by reactively pulsedDC magnetron sputtering in a first chamber. Then a seed layer and aferromagnetic free layer are formed 1002 by ion beam sputtering in thethird chamber. Then the remainder of a spin valve sensor through the AFMlayer is formed 1003 by DC magnetron sputtering in the fourth chamber.The tool 300 shown in FIG. 3b may be used, however one of the DCmagnetron sputtering chambers 301, 302 would not be used. Other tooldesigns may be used such as a tool having a single target DC magnetronsputtering chamber, a multitarget ion beam sputtering chamber and amultitarget DC magnetron sputtering chamber.

[0073] Alternative Embodiments

[0074] In the fabrication process of a spin valve head, a synthetic spinvalve sensor comprisingAl₂O₃(3)/Ni—Cr—Fe(3)/Ni—Fe(3)/Co—Fe(0.9)/Cu(2.4)/Co—Fe(0.8)/Ru(2.4)/Co—Fe(2)/Pt—Mn(22.5)/Ta(6)films (thickness in nm) is deposited in a manufacturing sputteringsystem comprising two loadlocks, one transportation module, twosingle-target DC magnetron sputtering chambers, one multitarget DCmagnetron sputtering chamber and one multitarget ion beam sputteringchamber.

[0075] The Al₂O₃ film is deposited on an Al₂O₃ (used as a bottom readgap) coated wafer with reactive pulsed-DC magnetron sputtering from ametallic Al target in 3 mTorr of mixed argon and oxygen gases in thefirst single-target DC sputtering module. An asymmetric bipolar pulsedDC power supply is used to provide target voltages of −200 and +50 Valternatively.

[0076] The Ni—Cr—Fe/Ni—Fe/Co—Fe films are then sequentially deposited ina xenon gas with a magnetic field of 40 Oe in the multitarget ion beamsputtering chamber. The Cu/Co—Fe/Ru/Co—Fe/Pt—Mn/Ta films are thensequentially deposited in an argon gas with a magnetic field of 40 Oe inthe multitarget DC magnetron sputtering chamber. The synthetic spinvalve sensor is annealed for 4 h at 260° C. in a magnetic field of 10kOe in a high vacuum oven to develop exchange coupling between the Co—Feand Pt—Mn films.

[0077] In contrast to the simple Ni—Mn spin valve sensor, the use of theNiO/NiMnO_(x)/Cu seed layers does not improve the GMR properties of thesimple Pt—Mn spin valve sensor. FIG. 12 and Table 3 show easy-axis MRresponses and magnetic properties, respectively, of the simple Pt—Mnspin valve sensors comprising seedlayers/Ni—Fe(4.5)/CoFe(0.6)/Cu(2.4)/Co(3.2)/Pt—Mn(22.5)/Ta(6) filmsafter anneal for 4 h at 260° C. with a field of 800 Oe in a high vacuumoven, where the seed layers are Ta(3), NiMnO_(x)(3) andNiO(33)/NiMnO_(x)(3)/Cu(1.4) films. The simple Pt—Mn spin valve sensorwith the Ta seed layer shows the best GMR properties. Since H_(UA) canonly reach ˜500 Oe, this H_(UA) must be amplified by utilizing thesynthetic spin valve design. TABLE 3 Magnetic and GMR properties ofsimple Pt—Mn spin valve sensors with various seed layers. NiO/NiMnO_(x)/Properties Ta NiMnO_(x) Cu H_(F) (Oe) 8.9 9.0 9.4 H_(UA) (Oe) 422 335322 R_(//) (Ω/Y) 17.0 18.1 18.1 GMR (%) 8.8 5.2 7.2

[0078]FIG. 13 and Table 4 show easy-axis MR responses and magneticproperties of synthetic spin valve sensors comprising seedlayers/Ni—Fe(3)/Co—Fe(0.9)/Cu(2)/Co(2.4)/Ru(0.8)/Co(2)/Pt—Mn(22.5)/Ta(6)films after anneal for 4 h at 260° C. with a field of 10 kOe in a highvacuum oven, where the seed layers are Ta(3), Ni—Cr—Fe(3),NiO(3)/Ni—Cr—Fe(3) and Al₂O₃(3)/Ni—Cr—Fe(3) films. The synthetic Pt—Mnspin valve sensor with the Al₂O₃/Ni—Cr—Fe seed layers exhibits magneticand GMR properties far better than those of the Pt—Mn spin valve sensorswith other seed layers. Hence, the combined uses of the reactivelyDC-pulsed sputtered Al₂O₃ and ion-beam sputtered Ni—Cr—Fe seed layersfor a synthetic Pt—Mn spin valve sensor substantially improve itsoverall GMR properties through specular scattering and grain coarsening,respectively. TABLE 4 Magnetic and GMR properties of synthetic Pt—Mnspin valve sensors with various seed layers. Al₂O₃/ Properties TaNi—Cr—Fe NiO/Ni—Cr—Fe Ni—Cr—Fe H_(F) (Oe) 9.0 3.3 44.3 3.9 H_(UA) (Oe)3637 3413 3610 3695 R_(//) (Ω/Y) 16.3 17.5 20.3 15.4 GMR (%) 8.0 9.1 5.912.2

[0079]FIGS. 14 and 15 show H_(F) and ΔR_(G)/R_(//), respectively, vs Cuspacer layer thickness for synthetic spin valve sensors comprising seedlayer/Ni—Fe(3)/Co—Fe(0.9)/Cu/Co(2.4)/Ru(0.8)/Co(2)/Pt—Mn(22.5)/Ta(6)films after anneal with a field of 10 kOe for 4 h at 260° C., where theseed layers comprise Ta(3), Ni—Cr—Fe(3), NiO(3)/Ni—Cr—Fe(3) andAl₂O₃(3)/Ni—Cr—Fe(3) films. The use of the Al₂O₃/Ni—Cr—Fe seed layerscauses a substantial H_(F) oscillation with the Cu spacer layerthickness, thereby leading to an H_(F) of as low as 3.9 Oe when the Cuspacer layer is as thin as 2 nm. In addition, the synthetic Pt—Mn spinvalve with the Al₂O₃/Ni—Cr—Fe seed layers exhibits a ΔR_(G)/R_(//) of ashigh as 12.2%, much higher than those with other seed layers.

[0080]FIG. 16 shows in-plane x-ray diffraction patterns of the simplePt—Mn spin valve sensor with the Ta seed layer before and after anneal.Before anneal, the Pt—Mn film exhibits a strong {220} crystallinetexture. After anneal, the Pt—Mn film exhibits a strong {111}_(fcc)crystalline textures and many other crystalline textures. Even without aPt—Mn {200}_(fcc) peak before anneal, Pt—Mn (200)_(fct), (020)_(fct) and(002)_(fct) peaks appear after anneal. In addition, the Pt—Mn{220}_(fcc) peak is split into Pt—Mn (220)_(fct), (202)_(fct) and(022)_(fct) peaks after anneal. These findings indicate that thetransformation from an fcc phase (a=0.3889 nm) to an fct phase (a=0.3997nm and c=0.3703 nm) has occurred in the Pt—Mn film. The change from astrong {220}_(fcc) crystalline texture to random crystalline texturesafter the phase transformation indicates that the fct phase may notexist before anneal and it prefers to nucleate and grow in its own way.The non-existence of the fct phase before anneal is supported by thefact that the Co—Fe and Pt—Mn films are not exchange-coupled at all(H_(UA)=0) before anneal.

[0081] In-plane x-ray diffraction patterns of the simple Pt—Mn spinvalve sensors with other seed layers before and after anneal also showsimilar characteristics, except that the {111}_(fcc) crystalline texturefor the simple Pt—Mn spin valve sensor with the Ta seed layers is muchmore stronger than the simple Pt—Mn spin valves with other seed layers.

[0082] In-plane x-ray diffraction patterns of the synthetic Pt—Mn spinvalve sensor before and after anneal show similar characteristics as thesimple Pt—Mn spin valve sensor before and after anneal, i.e., randomcrystalline textures of the Pt—Mn film after anneal. However, theintensity of the {111}_(fcc) crystalline texture is distinctly differentwhen different seed layers are used. The use of the Ta seed layer leadsto a strong {111}_(fcc) crystalline texture. This {111}_(fcc)crystalline texture substantially decreases when the NiO/Ni—Fe—Cr seedlayers are used, and substantially increases when the Al₂O₃/Ni—Cr—Feseed layers are used. Hence, it appears that a strong {111}_(fcc)crystalline texture is needed to exhibit good GMR properties.

[0083] It should be noted that when the reactively DC-pulsed magnetronsputtered Al₂O₃ seed layer is exposed to air, and the Ni—Cr—Fe seedlayer and other spin valve sensor films are deposited later, the GMRproperties are only the same as the synthetic spin valve sensor with theNi—Cr—Fe seed layer. Hence, it is crucial to maintain an in-situ smoothinterface at the Al₂O₃ and Ni—Cr—Fe seed layers to exhibit the best GMRproperties. This in-situ smooth interface is also needed tosubstantially reduce H_(F).

[0084] The use of reactive DC-pulsed magnetron sputtering for thedeposition of the Al₂O₃ film leads the Al₂O₃ film to provide an in-situsmooth surface. Due to this in-situ smooth surface, H_(F) oscillateswith the Cu spacer layer thickness, and an H_(F) of as low as 3.9 Oe anda GMR coefficient of as high as 12.2% can be attained when the Cu spacerlayer is as thin as 2 nm.

[0085] The reasons of each selected sputtering mode for each film arebasically the same as the Ni—Mn spin valve sensor. The only differenceis the use of the Co—Fe film, instead of the Co film as the pinnedlayer, since the H_(UA) of Co—Fe/Pt—Mn films (450 Oe) have been to foundto be higher than that of Co/Pt—Mn films (400 Oe).

What is claimed is:
 1. A method, comprising: a) forming an Al₂O₃ layerby reactive pulsed DC magnetron sputtering in a first chamber; b)forming over said Al₂O₃ layer a Ni—Cr—Fe/Ni—Fe/Co—Fe multilayerstructure by sequentially depositing: 1) said Ni—Cr—Fe layer by ion beamsputtering in a second chamber; 2) said Ni—Fe layer by ion beamsputtering in said second chamber; 3) said Co—Fe layer by ion beamsputtering in said second chamber; and c) forming over said multilayerstructure a remainder of a spin valve sensor through a Pt—Mnantiferromagnetic layer by DC magnetron sputtering in a third chamber.2. The method of claim 1 wherein said first chamber is a single targetchamber.
 3. The method of claim 1 wherein said second chamber is amulti-target chamber.
 4. The method of claim 1 wherein said thirdchamber is a multi-target chamber.
 5. The method of claim 1 wherein saidfirst chamber is a single target chamber, said second chamber is amulti-target chamber and said third chamber is a multi-target chamber,said first, second and third chambers each being part of the samesputtering system.
 6. The method of claim 1 wherein each of saidNi—Cr—Fe; Ni—Fe; and, Co—Fe layers are formed in Xenon gas within saidsecond chamber.
 7. The method of claim 1 wherein said remainder of aspin valve sensor is formed within Argon gas with said third chamber. 8.The method of claim 1 further comprising annealing said spin valvesensor.
 9. A spin valve sensor, comprising: a) an Al₂O₃ layer; b) aNi—Cr—Fe/Ni—Fe/Co—Fe multilayer structure over said Al₂O₃ layer; c) a Cuspacer layer over said multilayer structure; d) a Co—Fe/Ru/Co—Fe pinnedlayer over said Cu spacer layer; and e) a Pt—Mn antiferromagnetic layerover said pinned layer.